Current-limiting electric circuit breaker



4 Sheets-Sheet 1 J. F. JOHNSON ETAL CURRENT-LIMITING ELECTRIC CIRCUITBREAKER Filed NOV. 23, 1966 May 21, 1968 BVW G 7 May 21, 1968 F, JOHNSONET AL 3,384,845

CURRENT-LIMITING ELECTRIC CIRCUIT BREAKER Filed Nov. 23, 1966 4Sheets-Sheet 2 Arron/e) May 21, 1968 J. F. JOHNSON ET CURRENT-LIMITINGELECTRIC CIRCUIT BREAKER Filed NOV. 23, 1966 4 Sheets-Sheet 3 /A/ VE/VTORS c/osePH E dam/$0M, Pose/w M Lame/Mama? 21,. 16 J. F. JOHNSON E AL 99 CURRENTLIMITING ELECTRIC CIRCUIT BREAKER Filed Nov. 23, 1966 4Sheets-Sheet 4 //v Van mes. M0155! F Joya/$444 Foaerr M lm/aem/e/w/e/FUnited States Patent 3,384,845 CURRENT-LIMITING ELECTRIC CIRCUIT BREAKER.Ioseph E. Johnson, Plainville, and Robert W. Laubenheimer, Farmiugton,Conn, assignors to General Electric Company, a corporation of New YorkFiled Nov. 23, 1966, Ser. No. 596,637 6 Claims. (Cl. 335-23) Ourinvention relates to electric circuit breakers, and more particularly toelectric circuit breakers of the current-limiting type.

Electric circuit breakers of the current-limiting type referred toinclude three different means for causing opening of the contacts. Thefirst of these means is the manually-operable means (sometimesmotor-operated, subject to the control of an operator). The second ofthese means may be called conventional automatic opening means that is,means for causing opening or the contacts in response to abnormalcurrent conditions of medium and high value, such, for example as from125% to 300 600% of the nominal or maximum continuous current rating ofthe breaker. The third opening means is the ultrahigh speed orcurrent-limiting means which operates in response to short-circuitcurrents above the ZOO-600% nominal current range. In accordance withthe prior art, the manual-operating means and the conventional automaticopening means have ordinarily utilized the same basic mechanism. It isnot possible, however, to use this same mechanism for the performance ofthe currentlimiting contact opening action, since this must take placeat much higher speeds than the inertia of the manual operating mechanismwill permit. A circuit breaker of the type described which has provedparticularly effective in operation is disclosed, for example, inco-pending application S.N. 491,840 Heft, filed Sept. 30, 1965, nowPatent No. 3,315,189 and assigned to the same assignee as the presentinvention.

In accordance with the aforesaid Heft application, a latch or linkcarried by the contact operating arm of the manually operable mechanismis releasably held or latched in a first position in which it connectsthe contact operating arm to the operated movable contact. Acontact-opening force developed upon the occurrence of extremely highshort-circuit current conditions, is utilized to rotate this link withrespect to the contact arm to move it out of latched position, followingwhich it moves or translates, in straight-line manner, to anopen-circuit position. In elfect, a force-defeatable or break-awayconnection is provided such that although the movable contacts arenormally retained in closed circuit position by the manually operablemechanism with substantial contact pressure, nevertheless, if the forceacting on the contacts in opening direction becomes excessive, thecontact is, in effect, disconnected from the contact arm and permittedto move open without moving the relatively heavy parts of the operatingmechanism, and therefore without being required to overcome the inertiaof such parts.

In the construction disclosed in the aforesaid Heft application, certainmanufacturing and assembly problems were presented, largely because ofthe fact that the construction requires a double latch construction,i.e., one involving two latch pieces straddling the controlled contactoperating rod. In addition the over-all construction arrangement made itdifi'icult to assure consistent operation after a large number ofautomatic opening operations.

It is an object of the present invention to provide a current-limitingcircuit breaker mechanism of the type disclosed in the aforesaid Heftapplication which shall be easier to manufacture and assemble.

It is another object of the invention to provide a mechanism of the typedescribed which shall be capable of a ice greater number of operationswithout inconsistency of action.

In the drawings,

FIGURE 1 is a side elevation view of an electric circuit breakerincorporating the invention, portions of the casing being broken away todisclose the interior parts;

FIGURE 2 is a perspective view of some of the interior parts of thecircuit breaker of FIGURE 1;

FIGURE 3 is a semi-schematic illustration of the operating mechanism ofthe circuit breaker of FIGURE 1 the parts being shown in the positionthey occupy when the circuit breaker has been manually moved to the offposition;

FIGURE 4 is a semi-schematic illustration similar to FIGURE 3, the partsbeing shown in the position they occupy when the manually operableautomatically-operable mechanism is in closed condition, but thecontacts are opened by action of the high-speed opening means;

FIGURE 5 is a semi-schematic illustration similar to FIGURES 3 and 4,the parts being shown in the position they occupy when the manuallyoperable automaticallyoperable mechanism is in its tripped orautomatically opened condition;

FIGURE 6 is an enlarged detailed view of the contact operating rod ofthe circuit breaker of FIGURE 1; and

FIGURE 7 is a fragmentary semi-schematic illustration of a portion ofthe high-speed opening means of the invention.

Referring to FIGURE 1, the invention shown as incorporated in athree-pole electric circuit breaker comprising an outer enclosing casingof insulating material having a base It) and a cover 11. For purposes ofillustration, the casing is broken away to show the internalconstruction of the center pole of the circuit breaker. A line terminal12 is supported on the base on a conductive strap 13 suitably fixed tothe breaker base by suitable means, not shown. The terminal strap 13 isconnected to a first stationary contact support and are runner member 14supporting a first stationary contact 15. A second stationary contact 16is supported upon a similar confronting contact support and arc runnermember 17 supported in spaced relation to the member 14 by suitablemeans, not shown. The stationary contacts and 16 are interconnected by amovable bridging contact member 18 having contacts 19 and 20 thereonrespectively.

The contact support and arc runner member 17 has connected thereto oneend terminal portion 21 of a solenoid winding 22, the other end 23 ofwhich is electrically connected to a conductor strap 24%. The conductorstrap 24 is connected at its opposite end to a terminal member 25 of thetrip unit assembly 26, by suitable means such, for example, as the screw27. The terminal member 25 has one end of a generally inverted U-shapedheater strap 29 connected thereto by suitable means, such as by brazing,the other end of the heater 29 being connected to an output or loadterminal member 36, having a load terminal connector 31 supportedthereon. The parts and connections just described comprise the currentpath through the center pole of the circuit breaker. Similar partscomprising similar current paths, are provided in each of the outer twopoles of the circuit breaker.

Manual and conventional automatic operating mechanism As previouslydescribed, the circuit breaker of the present invention is adapted toperform the usual functions of automatic electric circuit breakers inpermitting the manually controlled opening and closing of contacts andalso in providing for the automatic opening of the contacts upon theoccurrence of sustained minor excessive current conditions or overloads,as well as for the automatic opening of the contacts upon the occurrenceof excessive current conditions higher than the moderate overloadcondition but less than a high short-circuit condition. For a IOU-amperebreaker, for example, overload conditions may be considered to be thosein the range or" 125 amperes to 600 amperes, while the high overloadlowshort-circuit excessive current conditions causin operation of theconventional magnetic means may be considered to be those lying in therange of 600 amperes to 3000 ampcres, and high short-circuit currentconditions may be considered as being those above 3000 amperes.

The manual and conventional automatic opening operating mechanism, whichis positioned in the central pole chamber of the circuit breaker andserves to operate the movable contacts of all three poles by gaugingmeans to be described, is indicated generally at 33 in FIGURE 1, andcomprises a pair of side plates or frames .34 (only one shown). The sideplates 34 serve to support a pivot pin 35 of a releasable member orcradle 36. The releasable member 36 is releasably held in the positionshown in FIGURE 1 by a latch member 3'7 pivotally supported on a pivotpin 38 carried by a bracket 39 mounted on the trip unit casing cover26A. A pair of upper toggle links 41 are positioned on opposite sides ofthe releasable member 35 and are connected thereto by a pin MA. A pairof lower toggle links 42, only one shown, are connected to the upperlinks 41 by a pin 45 at one end, and by a pin 45A to a pair of movablecontact actuator plates 45, which are pivotally supported with respectto the base 1 on a pivot shaft 46.

Referring to FIGURE 2, it will be observed that corresponding pairs ofcontact actuator plates 47, 47 and 48, 43 are also provided in each ofthe outer pole chambers for the purpose of operating the contact membersof the outside poles. The outer contact actuator plates #57, 47 and 48,48 are rigidly connected to the contact actuator plates 45, 45 by meansof an insulating tie bar 44.

Referring to FIGURE 1, a pair of tension springs 50 connect the toggleknee pin 49 to a generally U-shaped manually operable member 51 havingan insulating handle portion 52 projecting outwardly through an opening53 in the top wall. 11 of the casing. The springs 5b are connected tothe manually operable member 51 by means of pin 51A.

Manual operation In the position shown in FIGURE 1, the contact actuatorplates 45 of the central pole, as well as the contact actuator plates 47and 48 of the outer poles to which the plates 45 are connected by therigid interconnecting insulating cross-bar 44, are retained in onposition, holding the movable contacts in closed condition by a linkagesystem to be described. In order to move the contacts and mechanism tooff position, the operating handle 52 is moved toward the left as shownin FIGURE 1 from on" to off position. This moves the line of action ofthe springs 50 to the left of the pivot pin 41A interconnecting theupper toggle links 41 with the releasable member 36. This reverses thebias of the springs 50 on the links 41, and causes the toggle linkage tobuckle to the left and the parts to move to manual off position shown inFIGURE 3. It will be observed that in this position the contact actuatorplates 45 have rotated counterlockwise about the pivot 4-6. Since theouter plates 47 and 48 are rigidly connected to the central plates 45,they also move to corresponding open" position moving their contactslikewise to open position. The circuit breaker is closed by reversingthe movement of the operating handle 52, returning it to on position.

Automatic opening of the manually operable mechanism In accordance withthe invention, means is provided for causing the automatic opening ofthe manually operable operating mechanism 33 upon the occurrence ofoverload and low short-circuit currents. This means comprises anelongated bimetallic strip 54 for each of the poles of the circuitbreaker (only one shown) rigidly mounted at one end of the heater member29 and carrying an adjustable calibrating screw 55 at its free end. Eachof the calibrating screws 55 of the bimetallic strips 54 engages acommon trip bar 56 which is pivotally supported on a pivot pin 57supported in the trip unit casing, and biased for counterclockwiserotation by a spring 59. The common trip bar 56 also includes adepending portion 6t? at each pole location carrying a magnetic armaturemember 61 which is adapted to be attracted to a generally U-shapedmagnetic field piece 62 which embraces a portion of the heater conductor2). The depending portion 60 of the common trip bar 56 in the centerpole also has a latch surface 63 which serves to latch or releasablyrestrain an intermediate latch member 64 which is biased by a coil-typespring 65 in counterclockwise direction. The intermediate latch member64 includes a projection 64A which is disposed to strike a portion 37Aof the latch member 37 when the intermediate latch member is releasedfrom the latch surface 63. This causes clockwise rotation of the latchmember 37 and release of the end of the releasable member 36 from thelatch member 37. Since the line of action of the tension springs 50extends to the right of the pivot pin 41, upon the release of thereleasable member 36, the springs 59 rotate the releasable member 36 inclockwise direction, causing the projecting portions 418 of the uppertoggle links 41 to engage a stationary pin 34A carried by the framemembers 34. Further rotation of the releasable member 36 causesclockwise movement of the upper toggle links 41 with respect to thereleasable member 36, moving them to the final or tripped position shownin FIGURE 3. Since this action substantially shortens the distancebetween the pins 41A and 45A comprising the ends of the toggle linkage41-42, the contact actuator plates 45 are rotated counterclockwise bythis action as indicated in FIGURE 3. This action is translated intoopening movement of the contact in a manner to be described.

Upon the occurrence of short-circuit current conditions below the levelrequired to cause high-speed opening in the manner to be described, themagnetic field piece 62 becomes sufficiently energized to attract towardit the armature piece 61 carried by the trip bar extension 60. Thiscauses rotation of the trip bar 56, and release of the intermediatelatch member 64 with subsequent tripping action in the manner justdescribed. Following tripping operation, whether due to action of thebimetallic strip 54 or of the magnetic armature 61, the intermediatelatch is reset by moving the manually operable handle member 52 back toOh? position. This causes the bentover end portion 51A of the manuallyoperable member 51 to engage a portion of the releasable member 36 and'to rotate it in counterclockwise direction about its pivot 35 until thefree end portion thereof strikes the intermediate latch member 64rotating it clockwise about its pivotal support to relatched position. Afuller description of the latch mechanism described may be found inPatent 3,205,325, Sept. 7, 1965, H. W. Archer et al., assigned to thesame assignee as the present invention. The manually and automaticallyoperable operating mechanism per se is described in greater detail inPatent 3,155,803, issued Nov. 3, 1964, to K. W. Klein et al., andassigned to the same assignee as the present invention.

Current-limiting opening mechanism In accordance with the presentinvention, there is provided, in addition to the operating means formanually opening and closing the contacts and for automatically openingthe contacts upon the occurrence of overload and low short-circuitcurrent conditions, means for causing high-speed opening of the contactsat medium and high short-circuit current conditions, and for doing sosubstantially independently of the just described manual andconventional automatic opening mechanism.

For this purpose, a high-speed solenoid 22 is provided, included amagnetic plunger or armature 67 rigidly connected to a contact operatingrod 68. The contact operating rod 68 extends through a magnetic fieldpiece 69 or stator which also functions as a guide bearing positionedwithin one end of the coil 22 and at its forward portion is connected toan operating rod 70 carrying the movable contact member 18. The assemblycomprising the rod 70 and movable contact member 18 is movable withrespect to the main rod portion 68, being biased to the right as viewedin FIGURE 1 and FIGURE 6 by a compression spring 68' contained withinthe tubular rod 68, see FIGURE 6. One end of the spring 68 engages theend of the rod 70, and the other end engages a stop pin 70C carried bythe rod 68'. A lost-motion connection is provided between the rod 68 andthe rod 70 by means of the pin-and-slot arrangement comprising pin 70Acarried by the rod 70 and slot 70B in the tube 68. Following engagementof the contacts 19 and 20 with the stationary contacts and 16, continuedtravel of the rod or tube 68 compresses the spring 68 and moves the endof the slot 70B a short distance away from the pin 70A.

The rod 68 includes a separate end portion 68A to which it is connectedby an adjustable coupling member 68B which serves in the manner of aturnbuckle to vary the over-all length of the rod assembly to permitadjustment of the contact pressure, etc.

The end portion 68A is bifurcated and straddles a portion of ahigh-speed connecting link or latch member 73, to which it is connectedby means of the pin 71 extending through an elongated hole or slot 74 inthe latch 73 (see FIG. 1). A fixed pin 75 is also provided which isrigidly attached to the plates 34 of the mechanism frame of the centerpole. (While a single pin 75 is shown, we may use a pin-and-rollercombination to reduce friction.) Corresponding fixed pins 75A arecarried by frame members 76 for the outside poles, which are fixedlyattached to the base 10 by suitable means, not shown. The plates 45 areprovided with arcuate slots 76A providing clearance for the pin 75. Inaddition to providing such clearance, the ends of the slots 76 co-actwith the pin 75 to provide a stop or limit for the movement of theplates 45 in both the contact open and contact closed position. A slot77 is also provided in the latch 73 to permit limited movement of thispart with respect to the pin 75. The latch 73 includes a dependingangular portion 78 having a tension spring 79 connecting the remote endthereof with a spring anchor member 80. In addition, the latch 73includes two shoulder portions 82 and 83 and a hook portion 84, forpurposes to be described. If it is desired, of course, other suitablestop means may be used to limit the motion of the plates 45. In such acase, the pin 75 would be fixedly carried by either the plates 45 or thelatch 73, the other of such members being provided with a suitable slotto permit the required lateral movement or translation of the latch 73when rotated so as to disengage shoulder 82 from the roller 85.

The latch or link 73 is supported and guided for pivotal, sliding, orcombined pivotal-sliding movement between the plates 45 by means ofstepped insulating bushings of suitable material, preferably nylon, 85,and 86 (see FIGURES l, 3 and 4).

In the normal condition of the circuit breaker, as shown, for example,in FIGURE 1, the latch 73 functions simply as a connection between thecontact actuator plate assembly 45 and the contact rod assembly 68, bymeans of the pin 71 and roller 85. In other words, the plates 45comprise a driving member, the contact rod 68 comprises a driven member,and the roller 85 comprises a detent releasably engaged by. the latchmember 73 whereby the latch 73 forms an operative connection between theaforesaid driving and driven members. Thus, in FIGURE 1, the operatingsprings 50 and toggle links 41, 42, have rotated the contact actuatingplates 45 in clockwise direction about their pivot 46. A steel roller85B is carried by a pin 85A fixedly carried by the contact actuatorplates 45. A pair of nylon bushings 85 also Cal 6 carried by the pin 85Ahelp to guide the latch 73 in it movements.

In the normal condition as shown in FIGURE 1, the latch 73 is biased bythe tension spring 79 clockwise about the pin 75, retaining the shoulder82 in engagement with the steel latch roller 85B. The clockwise movement of the contact actuator plates 45, from the position shown in FIG.3 to the position shown in FIG. 1 there fore carries with it the latch73.

When the operating handle is moved to off or tripped position, thecontact actuator plates 45 are rotated counterclockwise to the positionshown in FIGURE 3. As the actuator plates 45 rotate, the latch roller85B moves into engagement with the hook portion 84 of the latch 73 andcarries the latch 73, and through it the contact rod 68A, to the offposition as shown in FIGURE 3.

When the parts are in the closed circuit position as shown in FIGURE 1,if a high short-circuit condition occurs, the solenoid 22 becomessufliciently energized to draw the magnetic armature or plunger 67 tothe left as viewed in FIGURE 1 at high speed. This motion is transmittedto the latch 73 by means of the connection of the pin 71 in the slot 74.This causes the latch 73 to rotate counterclockwise about the pinagainst the tension of the spring 79, moving the shoulder 82 down belowthe latch roller 858. When this rotation has occurred suificiently topermit the shoulder 82 to clear the roller 85, the entire latch 73translates or slides to the left as viewed, under both the influence ofthe spring 79 and the force of the solenoid 22. The parts then assumethe relative positions as shown in FIGURE 4, with the latch roller 85Bin engagement with the second shoulder 83.

It will be observed that the contact actuator plates 45 have not movedfrom their normal on position as shown in FIGURE 1. It will be recalledthat this position is determined by the action of the pin 75 in the endof the slot 76 limiting clockwise motion of the actuator plates 45.

Tripping of conventional mechanism and resetting of high-speed linksAlthough the highspeed tripping action caused by the solenoid 22 takesplace independently of the main operating mechanism, and before movementof the main operating mechanism toward tripped condition, the currentlevels required for actuation of the solenoid 22 are above the currentlevel required for actuation of the magnetic tripping means 62-61.Accordingly, substantially simultaneously with the movement of theplunger 67, the armature 61 is attracted to the field piece 62, causingrelease of the intermediate latch member 64. This in turn causes releaseof the main latch 37 and tripping of the main mechanism in the mannerpreviously described. Because of the number of ditferent parts involvedand their mass, as well as the chain reaction sequence of movementsrequired, tripping of the conventional or manually operable mechanism isnot completed until after the high speed opening of the contacts hasalready taken place. When tripping of manually operable mechanism doesoccur, however, the mechanism parts move to the tripped condition asindicated in FIGURE 5. It will be observed that as the conventionalmechanism moves to its tripped position, the contact actuator member 45moves counterclockwise to its fully opened position (compare theposition of this part in FIGURE 5 to the position of the same part inFIGURE 3, for example). As the contact actuator plates 45 are rotatedcounterclockwise as viewed, and once again gets behind the shoulder 82resetting that latch 73. Note that the latch 73 is prevented from movingfurther to the left by the engagement of the end of slot 77 with pin 75,and also that the latch 73 is biased clockwise at all times by spring79.

The arrangement by which the armature 67 is directly connected, by a pin70A, to the movable contact member 70, has the result that the movablecontact member moves toward open position as soon as the armature moves.Thus there is no time lag after the armature 67 begins to move beforethe movable contacts begin to move. The aspects of the movable contactassembly by which this is made possible are the invention of E. B. Heftand R. W. Laubenheimer and are covered in copending application Ser. No.597,118 filed Nov. 25, 1966 and assigned to the same assignee as thepresent invention.

It will be observed, that the fixed pin 75 serves several functions.First, it serves as a pivot support for the link 73 in the normallatched condition of the link 73, when the tension spring '79 is pullingon the extension 73. This maintains the opposite end of the link 73 inengagement with the roller 85B and maintains the roller 85B behind theshoulder 82. Secondly it serves, in combination with the grooved rollersor bushings 85 and 86, to slidably guide the link 73 during itstranslating movement to the left during high-speed tripping. Thirdly, itserves as a stop to limit movement of the contact actuator plates 45 inboth the closed and open directions, by engagement with correspondingends of the slot 76. Finally, it serves to restrain movement of thehigh-speed link 73 to the left while resetting is occurring, in themanner just described.

By reason of the particular novel configuration of the latch 73, it willbe observed that the surfaces of the highspeed link 73 which arecritical, that is, the surface of the shoulders 82 and 83, are readilyaccessible for machining and polishing to provide the required accuracy.This would not be the case if these surfaces were formed, for example,as portions of one or more closed slots.

The basic relation of the forces acting on the latch 73 is shown inFIGURE 7. As indicated, a component of the force originating in mainmechanism springs 50 is exerted by the roller 85B on the latch member asforce F-l. The greater part of this force is transmitted by the latchmember 73 to the pin 71 and the contact rod 68 as contact closing forceF-l. An equal and opposite force F-Z is, of course, exerted by the pin71 on the latch 73.

In addition, the force F-3 of the solenoid 22 is always acting incontact opening direction on rod 63. Normally this force isinsignificant. On high short-circuit conditions, however, this forcebecomes substantial, and, adding to the reaction force F-Z, produces atorque tending to rotate the latch 73 counterclockwise about the pin 75which is then great enough to exceed the clock-wise torque constantlyexerted by the force 1 -4 of spring 79 on latch 73. As a result, thelatch rotates counterclockwise, moving the shoulder 82 below the roller85B and permitting lateral translation of the latch 73 to the left,opening the contacts. This movement is also assisted by the spring 79,cooperating with the solenoid 22 and with blow-off forces between thecontacts.

While the invention has been disclosed in only one particularembodiment, it will be readily apparent that many modifications thereofmay readily be made. It is therefore intended by the appended claims, tocover all such modifications as fall within the true spirit and scope ofthe invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A current-limiting electric circuit breaker comprising:

(a) asupport;

(b) at least one pair of relatively movable contacts supported on saidsupport;

() contact operating means supported on said support;

.(d) connecting means connecting said contact operating means to saidrelatively movable contacts for operating said contacts between open andclosed circuit positions;

(e) said connecting means comprising a driving member operably connectedto said contact operating means and a driven member operably connectedto said relatively movable contacts;

(f) means releasably interconnecting said driving and driven memberscomprising detent means carried by one of said driving and drivenmembers and latching means connected to the other of said driving anddriven members, said latching means having a portion engaging saiddetent means when said latching means is in a predetermined normalposition;

(g) a pivot pin supporting said latching means for pivotal movement awayfrom said normal position upon the exertion of predetermined forceexerted on said driven member in contact-opening direction said pivotpin being fixed with respect to both said driving and driven members,and

(11) current responsive means for exerting said predetermined force onsaid driven member in contact opening direction upon the occurrence ofpredetermined eurrent conditions through said contacts, said latchingmeans moving out of engagement with said detent means upon theoccurrence of said predetermined force and permitting movement of saiddriven member in contact opening direction substantially independentlyof said contact operating means.

2. A current-limiting electric circuit breaker as set forth in claim 1wherein said driving member includes a pair of spaced abutments, saidabutments engaging said fixed pivot pin and limiting travel of saiddriving member in contact opening and closing direction respectively.

3. A current-limiting electric circuit breaker as set forth in claim 1wherein said detent means comprises a roller carried by said drivingmember and said latching means comprises a latch member having anelongated slot therein, said pivot pin extending through said slot andcooperating with the ends of said slot to limit movement of said latchmember with respect to said pin, said latch member also including anabutment engaging said roller, and spring means normally biasing saidlatch member for pivotal movement about said pivot pin to maintain saidabutment in engagement with said roller.

4. A current-limiting circuit breaker comprising:

(a) asupport;

(b) at least one pair of relatively movable contacts supported on saidsupport;

(0) contact operating means supported on said support;

(d) connecting means connecting said contact operating means to saidrelatively movable contacts for operating said contacts between open andclosed circuit positions;

(e) said connecting means comprising a driving member operably connectedto said contact operating means and a driven member operably connectedto said relatively movable contacts;

(f) means releasably interconnecting said driving and driven memberscomprising detent means carried by one of said driving and drivenmembers and latching means connected to the other of said driving anddriven members, said latching means having a portion engaging saiddetent means when said latching means is in a predetermined normalposition;

(g) a pivot pin supporting said latching means for pivotal movement awayfrom said normal position upon the exertion of predetermined forceexerted on said driven member in contact-opening direction;

(h) current-responsive means for exerting said predetermined force onsaid driven member in contact opening direction upon the occurrence ofpredetermined current conditions through said contacts, said latchingmeans moving out of engagement with said detent means upon theoccurrence of said predetermined force and permitting movement of saiddriven member in contact opening direction substantially independentlyof said con-tact operating means;

(i) said contact operating means comprising a member movablereciprocally between open and closed circuit positions;

(j) said latching means comprising a single latch memoer having a slottherein through which said pivot pin extends;

(k) said detent means comprising a roller carried by one of said latchmember and said driving member and a cooperating first abutment carriedthe other of said latch means and said driving member, and

(1) means pivotally connecting said contact operating member and saidlatching member.

5. A current-limiting circuit breaker as set forth in claim 4 whereinsaid one of said latch member and said driving member also includes asecond abutment spaced from said first abutment and engageable by saidroller upon movement of said driving member from said closed toward saidopen position.

6. A current-limiting circuit breaker as set forth in claim 1 whereinsaid contact operating means comprises means for manually operating saidcontact operating means for operating said contacts between open andclosed circuit positions and second current responsive means forautomatically moving said contacts from said closed to said openposition upon the occurrence of predetermined second current conditions.

References Cited UNITED STATES PATENTS 2,601,484 6/1952 Wood 335-463,012,118 12/1961 Edmunds 33516 3,315,189 4/1967 Heft et a1 33516BERNARD A. GILHEANY, Primary Examiner.

H. BROOME, Assistant Examiner.

1. A CURRENT-LIMITING ELECTRIC CIRCUIT BREAKER COMPRISING: (A) ASUPPORT; (B) AT LEAST ONE PAIR OF RELATIVELY MOVABLE CONTACTS SUPPORTEDON SAID SUPPORT; (C) CONTACT OPERATING MEANS SUPPORTED ON SAID SUPPORT;(D) CONNECTING MEANS CONNECTING SAID CONTACT OPERATING MEANS TO SAIDRELATIVELY MOVABLE CONTACTS FOR OPERATING SAID CONTACTS BETWEEN OPEN ANDCLOSED CIRCUIT POSITIONS; (E) SAID CONNECTING MEANS COMPRISING A DRIVINGMEMBER OPERABLY CONNECTED TO SAID CONTACT OPERATING MEANS AND A DRIVENMEMBER OPERABLY CONNECTED TO SAID RELATIVELY MOVABLE CONTACTS; (F) MEANSRELEASABLY INTERCONNECTING SAID DRIVING AND DRIVEN MEMBERS COMPRISINGDETENT MEANS CARRIED BY ONE OF SAID DRIVING AND DRIVEN MEMBERS ANDLATCHING MEANS CONNECTED TO THE OTHER OF SAID DRIVING AND DRIVENMEMBERS, SAID LATCHING MEAND HAVING A PORTION ENGAGING SAID DETENT MEANSWHEN SAID LATCHING MEANS IS IN A PREDETERMINED NORMAL POSITION; (G) APIVOT PIN SUPPORTING SAID LATCHING MEANS FOR PIVOTAL MOVEMENT AWAY FROMSAID NORMAL POSITION UPON THE EXERTION OF PREDETERMINED FORCE EXERTED ONSAID DRIVEN MEMBER IN CONTACT-OPENING DIRECTION SAID PIVOT PIN BEINGFIXED WITH RESPECT TO BOTH SAID DRIVING AND DRIVEN MEMBERS, AND (H)CURRENT RESPONSIVE MEANS FOR EXERTING SAID PREDETERMINED FORCE ON SAIDDRIVEN MEMBER IN CONTACT OPENING DIRECTION UPON THE OCCURENCE OFPREDETERMINED CURRENT CONDITIONS THROUGH SAID CONTACTS, SAID LATCHINGMEANS MOVING OUT OF ENGAGEMENT WITH SAID DETENT MEANS UPON THEOCCURRENCE OF SAID PREDETERMINED FORCE AND PERMITTING MOVEMENT OF SAIDDRIVEN MEMBER IN CONTACT OPENING DIRECTION SUBSTANTIALLY INDEPENDENTLYOF SAID CONTACT OPERATING MEANS.